1. Field of the Invention
The present invention relates to optical fibers having low bend losses.
2. Technical Background
A long standing need exists for low bend loss optical fibers, particularly for optical fibers utilized in so-called “access” and fiber to the premises (FTTx) optical networks. Optical fiber can be deployed in such networks in a manner which induces bend losses in optical signals transmitted through the optical fiber. Some applications that can impose physical demands, such as tight bend radii, compression of optical fiber, etc., that induce bend losses include the deployment of optical fiber in optical drop cable assemblies, distribution cables with Factory Installed Termination Systems (FITS) and slack loops, small bend radius multiports located in cabinets that connect feeder and distribution cables, and jumpers in Network Access Points between distribution and drop cables.
Optical fiber is typically cabled such that an optical fiber or a bundle of optical fibers is surrounded by a buffer tube and/or matrix material. For example, a co-planar bundle of optical fibers can be encapsulated into a ribbon cable matrix. Optical fiber may be disposed in loose tubes, and the loose tubes in loose-tube cable can be unfilled or filled with a buffer material such as gel. Optical fiber may instead be tightly buffered by encasing the fiber in a plastic layers, such as a soft plastic layer surrounded by a hard plastic layer. Other cabling is known.
The MAC number of an optical fiber, as used herein, is defined as the mode field diameter at 1310 nm, in microns, divided by the fiber cut-off (according to the 2 meter test), in microns. See, for example, Unger and WO 01/27667. It is known that optical fibers having lower MAC numbers will generally exhibit lower macrobend losses.
Increasingly, coarse wavelength division multiplexing (CWDM) systems and applications operate in the 1310 nm window, the S-band, C-band, and/or L-band. Low bend losses are desirable in optical systems with various bending environments imposed upon optical fiber such as found in access and FTTx optical network deployments, particularly in each of the 1310 nm window and S-, C-, and L-bands.